1. Field of the Invention
The present invention relates to method of inspecting a flat panel display, and more particularly, to method of inspecting a partial stain of a flat panel display.
2. Description of the Related Art
A partial stain of a flat panel display is an image that looks like a spot on a part of the screen of the flat panel display due to non-uniformity of brightness. In order to inspect the partial stain, it is a usual operation to output a test image to a display panel and analyze the state of the test image. There are manual and automatic inspection methods for analyzing the state of the test image.
The manual inspection method is for a professional inspector to find and evaluate the stain visible to the naked eye. By this method, the inspector's subjective decision about the quality of the panel can not guarantee the qualitative uniformity of the panel. The manual inspection method has some problems. For example, the process speed of the manual inspection is not as fast as that of an automatic inspection method. Moreover, it is very difficult for the inspector to obtain the required skill of detection to the level of dependability.
Meanwhile, the automatic inspection method is performed by obtaining the test image on the panel with a photographing apparatus, like a camera, and detecting the defect through an image processing operation. The image processing operation includes detecting the brightness information from the test image obtained by the camera and comparing it with a predetermined brightness reference. As a result of the comparing operation, the defect of the panel is determined according to whether the difference of the comparison between the brightness information and the brightness reference is beyond a permitted limit.
The brightness reference in the image procession is constantly applied to all of the panels to be inspected. However, the partial stain is due to a relative brightness difference according to the location on the screen, not due to an absolute brightness beyond the brightness reference. Further, because the brightness characteristic of the panel affects the real brightness, detecting the defect must be evaluated relatively according to each panel. Therefore, the conventional automatic method for inspecting a flat panel display, which constantly applies one brightness reference to all of the panels, does not guarantee the accuracy of the detection of the defects.